Management of pulmonary edema and interstitial diseases of the lung is impaired by lack of accurate non-invasive means to monitor altered lung permeability and lung water content. In dogs and normal humans, we will evaluate a method to assess lung epithelial permeability from the rate of clearance from the lung of inhaled aerosols containing lipophobic radioactive tracers. Gamma cameras will be used to measure total and regional clearance rates. Rate of arrival in blood and non-pulmonary tissues will be monitored to detect altered permeability and the influence of background counts on observed lung clearance. Potential sources of variability in the technique such as aerosol size, site of deposition in the lungs, volume of gas in the lungs, and pulmonary vascular pressures will be determined in order to develop the most precise means to detect alterations from high permeability pulmonary edema and cardiogenic pulmonary edema. The index developed from these studies will be applied to patients with interstitial lung disease to see if it can supplement or replace bronchopulmonary lavage, gallium scans, and other means to detect alveolitis. The rebreathing method using soluble gases for non-invasively measuring lung water and cardiac output will be evaluated in normal humans using different breathing maneuvers and sampling techniques that will minimize errors from uneven distribution of the test gas in the lungs. The accuracy of this technique will be determined by making these measurements in patients with cardiopulmonary diseases having indicator dilution cardiac output measurements and chest computerized tomograms from which lung weight can be calculated. Tests of lung function in these patients including flow rates, indices of ventilation to volume mismatching, and impaired gas exchange will be analyzed to determine what degree of altered lung function causes significant errors in the rebreathing measurements of cardiac output and lung water. These studies are directed at defining the degree of cardiopulmonary dysfunction that does not interfere with non-invasive rebreathing measurements of cardiac output and lung water.